Conventionally, in a fuel injection control device for an internal combustion engine, a fuel pressure sensor that detects fuel pressure inside of a fuel supply passage is disposed, and an injection characteristic of a fuel injector is learned based on the fuel pressure detected by the fuel pressure sensor. For example, Patent Literature 1 discloses such kind of fuel injection control device.
The fuel injection control device disclosed in Patent Literature 1 has correction parameters corresponding to cylinders respectively and determines a fuel injection amount of each cylinder by multiplying a basic fuel injection amount set in advance by each of the correction parameters of the cylinders. The fuel injection control device learns the correction parameter of each cylinder based on the fuel pressure detected by the fuel pressure sensor. Specifically, the fuel injection control device detects the fuel pressure by the fuel pressure sensor at each 180° CA (Crank Angle). The fuel injection control device calculates a drop amount of the fuel pressure in accordance with a fuel injection from the fuel pressure detected by the fuel pressure sensor in each cylinder and learns the correction parameter based on the drop amount of the fuel pressure calculated in each cylinder.
In recent years, in the internal combustion engine, so-called divided injection in which a fuel injection is divided into a plurality of times of fuel injection is performed in order to reduce emissions or improve fuel consumption. In a case in which the divided injection is performed by the fuel injection control device disclosed in Patent Literature 1, for example, when a time period from a start to an end of the divided injection becomes longer than 180° CA, the fuel pressure may be detected by the fuel pressure sensor during the fuel injection of the fuel injector. When the fuel pressure is detected during the fuel injection, it is impossible to appropriately detect the drop amount of the fuel pressure in accordance with the fuel injection, and therefore the learning described above may not be performed appropriately.